The present invention relates to a device for fastening poles, posts, masts or the like in the ground and a method for manufacturing a fastening device.
Fastening devices for poles, posts, masts or the like for driving or screwing into the ground are in most cases manufactured by metal casting or welding together individual prefabricated shaped parts. In this connection, the manufacture of parts by casting or milling is relatively complicated and costly, and the manufacture of shaped parts does not allow 100% utilization of the starting material, which likewise contributes to increasing the cost of manufacture. In addition, the joints, at which the individual shaped parts are welded, adhesively bonded or pressed together, may bring about a weakening of the stability of the basic bodies of the corresponding fastening devices.
A fastening device is known from German Utility Model 93 13 258.1. This has a threaded portion, which can be screwed into the ground and out of it again, and a holding portion for receiving the pole, post, mast or the like. A cone-shaped displacement body for the earth material, which is active when the fastening device is screwed in, is arranged between the threaded portion and the holding portion. The threaded portion is a cast part and bears a spiral-shaped thread. The adjacent displacement body is shaped like a truncated circular cone and is essentially hollow and is, on the side of its smaller diameter, welded to the essentially cylindrical or slightly conical solid core of the threaded portion. The cone angle of the truncated circular cone-shaped displacement body is in this case distinctly greater than the angle of the threaded portion. The threaded portion and the displacement body form the anchoring portion of the fastening device.
As the fastening device, and in particular the anchoring portion, according to German Utility Model 93 13 258.1, is made up of a number of parts welded together, problems of strength may arise in particular in the region of the connection between the threaded portion and the displacement portion during screwing-in and out or in the event of forces acting on the fastening device. Moreover, the threaded portion of the anchoring portion, which is in the form of a cast part with a solid core, requires the use of a great deal of material.
Another fastening device is described in German patent specification 40 02 830. This fastening device has a threaded portion which can be screwed into the ground and out of it again and, at its rear end seen in the screwing-in direction, a holding portion for receiving the pole, post or the like is provided. The threaded portion, which is designed as the anchoring portion, is of corkscrew-like or screw-like design and has a conical core which tapers steeply in the screwing-in direction. The relatively obtuse cone angle, which remains constant over the entire anchoring portion, makes screwing the fastening device into the ground more difficult on account of radial forces which arise, and, owing to the cone shape, does not allow secure anchoring of the fastening device in the ground because forces, such as those caused by shaking movements, arising radially on account of the obtuse cone angle, lead to the anchoring portion being loosened from the ground.
The fastening device according to German patent specification 40 02 830 consists of plastic material, which requires manufacture by laminating, hot-forming, injection moulding etc. These processes are relatively cost-intensive and thus expensive on account of necessary preliminary work. While it is true that an anchoring portion manufactured in this way does not have any stability-reducing joints, it nevertheless has to be made from solid material in order to achieve the stability required.